/*
 * Copyright (c) 2010, 2011, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package java.lang;

import java.util.concurrent.ConcurrentHashMap;

public abstract class ClassValue<T> {
    private final ConcurrentHashMap<Class<?>, T> cache = new ConcurrentHashMap(128);

    public ClassValue() {
    }

    protected abstract T computeValue(Class<?> type);

    public T get(Class<?> cls) {
        T obj = this.cache.get(cls);
        if (obj != null) {
            return obj;
        } else {
            synchronized (this) {
                obj = this.cache.get(cls);
                if (obj != null) {
                    return obj;
                } else {
                    obj = this.computeValue(cls);
                    this.cache.put(cls, obj);
                    return obj;
                }
            }
        }
    }
}
